The present invention relates to a right-left driving force control system and more particularly to a right-left driving force control technique for maintaining a stable vehicle behavior.
A driving force distributing system has been developed in which a yaw moment acting on a vehicle is controlled by generating a difference in driving force between right and left wheels when the vehicle is making a turn, so as to increase the turning performance of the vehicle.
In such a related-art driving force distributing system, however, although a driving force difference can be generated between the right and left wheels, the driving force difference cannot be limited, leading to a problem that the slippage of right and left drive wheels cannot be suppressed when the vehicle is running straight ahead.
In view of the above problem, another related art of a right-left driving force distributing system has been developed. The right-left driving force distributing system includes a right-left driving force adjusting unit and a differential action limiting unit (refer to JP-A-2008-298191).
In a related-art right-left driving force distributing system like the one described in JP-A-2008-298191 in which a differential action limiting unit is provided in a right-left driving force adjusting unit, a control becomes necessary to use the right-left driving force adjusting unit and the differential action limiting unit independently.
As a conceived controlling approach, an approach can be considered in which a driving force adjusting amount by the right-left driving force adjusting unit and a differential action limiting amount by the differential action limiting unit are calculated individually from a running state of the vehicle, so as to control the right-left driving force adjusting unit and the differential action limiting unit separately.
However, in the approach described above, there is a fear that the right-left driving force adjusting unit and the differential action limiting unit happen to be used concurrently. In the event that the right-left driving force adjusting unit and the differential action limiting unit are used concurrently, there is caused a torque interference due to interlocking, resulting in a problem that the operation efficiency and controllability of the driving force distributing system are reduced.
Although an approach can be considered to prevent such a concurrent operation of both the units in which the right-left driving force adjusting unit and the differential action limiting unit are switched over selectively so that only either of them can be put into operation, there is caused a fear that a drastic change in driving force difference takes places when the right-left driving force adjusting unit and the differential action limiting unit are so switched due to the magnitudes of right-left driving force adjusting amount and differential action limiting amount being different and the behavior of the vehicle becomes discontinuous. In addition, while the vehicle is running straight ahead, the difference in wheel speed between the right and left wheels is frequently reversed left to right or vice versa, and when this happens, so-called hunting is generated between the right-left driving force adjusting unit and the differential action limiting unit, and consequently, there is caused a fear that the behavior of the vehicle becomes discontinuous.